1. Field of the Invention
This invention relates to a method of magnetic recording, and more particularly to improvements made in the recording method so as to exclude dropout from a reproduced output.
2. Description of the Prior Art
Recording using a silver-halide photographic film has recently been gradually replaced by recording using a disk-shaped or card-like magnetic recording sheet on which still pictures are electronically recorded. Especially, standardization of the so-called magnetic disk cameras using a magnetic disk is now being attempted for their commercial practical use. This magnetic disk carema comprises an integral combination of an image pick-up device such as a solid-state image pick-up element or an image pick-up tube and a magnetic disk type recording device. More precisely, as shown in FIG. 5, an optical image of an object 2 is picked up in the form of a still picture by an image pick-up unit 3 through a lens 1, and, after a raster scan type picture signal generated from the image pick-up unit 3 is subjected to signal processing including frequency modulation in a signal processing circuit 6, an output signal of the signal processing circuit 6 is applied through a recording amplifier 7 to a recording magnetic head 5 to be recorded on a circular track on a rotating magnetic disk 4. The magnetic disk 4 is rotated by a drive unit 8, and a position of the magnetic head 5 on the magnetic disk 4 is determined by a head positionning unit 9. A system for reproducing such a magnetically recorded still picture comprises an integral combination of a magnetic disk type reproducing device and picture display unit such as a television set or a hard copy dispensing unit such as a printer. More precisely, as shown in FIG. 6, a predetermined track on a rotating magnetic disk 4 is repeately scanned by a reproducing magnetic head 10, and, after an output signal of the magnetic head 10 is applied through a reproducing amplifier 14 to a signal processing circuit 15 to be subject to signal processing including demodulation, an output signal of the signal processing circuit 15 is applied to, for example, a television set 11 to display a visible picture or a soft copy on its display screen. Alternatively, the output signal of the signal processing circuit 15 is applied to a printer 12 to be printed out on a recording sheet 13 to provide a hard copy. The magnetic disk 4 is rotated by a drive unit 16, and a position of the magnetic head 10 on the disk 4 is determined by a head positioning unit 17.
When dropout occurs or is included in the reproduced output of the magnetic head 10 during reproduction of a still picture, such an output is applied to the television set 11 to be displayed on the display screen. However, since the same still picture signal is repeatedly reproduced for the purpose of display, the dropout appears repeatedly on the same portion of the reproduced still picture, resulting in a very indecent display. Such a situation is also inevitable in the case of a hard copy printed out by the printer.
As is commonly known, occurrence of such dropout is mainly attributable to various defects inherent to a magnetic recording medium, for example, an uneven surface or surface roughness of a supporting base, scars present on the surface of a magnetic material layer and attachment of dust to the surface of the magnetic material layer. Therefore, once dropout has occurred on a track, the dropout would not disappear in most cases even when the still picture signal is recorded again on the same track.
With a view to utilize only such a track which is dropout-free, Japanese patent Application Lay-Open Print No. 51-82516(1976) discloses an idea according to which "when a certain still picture signal is recorded on a certain track, the recorded signal is immediately reproduced, and, if dropout is detected in the reproduced output, the still picture signal recorded immediately before is recorded again on the next adjacent track." Also, this Lay-Open Print discloses an idea according to which "an address number for the purpose of track search is not recorded on the track from which dropout has been detected". Thus, in the playback mode, a track including dropout is automatically skipped so that dropout-free normal pictures only can be succesinely reproduced. The proposed recording method is effectively applicable to the case where many frames of photographic pictures recorded on a conventional silver-halide photographic film or printed on sensitized papers are re-recoreded on a magnetic recording medium in a desired order so that the magnetic recording medium replaces on a photographic album. Especially, a merchant now engaging in the D.P.E(developing, printing and enlarging) business will expect that a business of making an album of pictures using a magnetic recording medium will appear in future. When appearance of such a business is expected, arranging many frames of photographic pictures in the order specified by the user is required, in addition to the guarantee of the good picture quality. Therefore, the aforementioned method of magnetic recording dealing with the problem of occurrence of dropout is quite useful.
However, the prior art method described above is based on the premise that a special address number is recorded at a leading end or trailing end of each track for the purpose of facilitating track search. Therefore, the proposed method is disadvantageous more or less in the following points:
(1) The address number is an address identification signal provided for identification of the corresponding still picture signal. Therefore, the circuit structure of the recording system becomes complex due to the necessity for recording such additional signal.
(2) For specifying the individual tracks, address numbers having different contents respectively must be recorded, resulting a more complex circuit structure.
(3) In the event of occurrence of dropout in the recorded area of an address signal, it is impossible to search the corresponding track. This is attributable to the fact that the presence or absence of dropout is checked for only the recorded area of the still picture signal, and, when the result of checking proves that no dropout is present, the address number is additionally recorded.